R.W. HOBSON, R.J. HARTMAN AND E.W. KANNING
2094
[CONTRIBUTION FROM THE
DEPARTMENT OF CHEMISTRY OF
Vol. G3
INDIANA UNIVERSITY ]
A Solubility Study of Di-n-propylamine BY R. W. HOB SON,^ R.J. HARTMAN AND E. W. KANNING
A less common type of binary liquid system is that which has a lower consolute temperature. I t has been noted2 that almost invariably this type consists of either a hydroxy compound and an amine, or a hydroxy compound and a compound containing a keto or ether group. For example, the systems diethylamine-water,3 triethylamine-water,* and monoethers of ethylene glycol and water6 exhibit this behavior. The last type also have upper consolute temperatures. It was the purpose of this investigation to construct the solubility curves for the binary system di-n-propylamine-water and the ternary system di-n-propylamine-water-ethanol.
-5
4-5
Fig. 1.-Mutual
25 35 45 55 65 75 Temp., "C. solubility curve for the system di-npropylamine-water. 15
Experimental Materials.-The di-n-propylamine was obtained from the Eastman Kodak Co.; upon analysis it was found to be 99.9% pure. Pure water was prepared using the same pro(1) 'Phis paper i s constructed from the thesis submitted by R . W , Hobson in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Indiana University, June, 1941. (2) See S. Glasstone, "Textbook of Physical Chemistry," D. Van Nostrand C o . , New York, N.Y.,1940, p. 718. ( 3 ) Lattey, Phil. M a g . , [61 10, 397 (1905); see also Guthrie, i h i d . , 15) 18, 1 2 , 105, 495 (1886) (1) Kothrnund, %. p h y s i k . C h e v . , 26, 459 (1898). ( 5 ) Cox and Cretcher, THISJ O U R N A L 48, , 431 (1926); Cox, ibid., 4S, 1080 (1927).
cedure as is followed in making conductivity water. Absolute alcohol was prepared by refluxing with calcium oxide, followed by triple distillation. Procedure.-Alexejeff's synthetic method6 was followed in studying the di-n-propylamine-water system. All temperatures were read from a calibrated Beckmann thermometer. For temperatures below 15", the determinations were carried out in an unsilvered dewar flask. The bath was air-stirred and cooled by adding very small portions of chipped ice and salt. The modified titration method of Walton and Jenkins' was followed in determining the data for the amine-alcohol-water system. AI1 temperatures were read from a calibrated Beckmann thermometer.
The data obtained for the system di-n-propylamine-water are shown in Table I and the solubility curve for this system in Fig. 1. The characteristic blue opalescence associated with compositions lying near that of the critical solution temperature was observed slightly below the critical solution temperature (sample 8 in Table I). The critical solution temperature was found to be -4.8' (below that of diethylamine (143.5') and triethylamine (18.5')). The composition a t this temperature is approximately 34% amine and 66% water. In those samples containing only a few per cent. of amine that are homogeneous a t room temperature, some colorless particles (possibly hydrate crystals) were observed. The sample containing 33.G9% ainine and 66.31y0 water was heated in an air-bath. Two layers could still be noted a t the critical temTABLE I MUTUAL SOLUBILITY OF DI-%-PROPYLAMINEAND WATER AT VARIOUSTEMPERATURES % amine
Weight
T p p C.
1.96 2.42 2.91 5.86 9 33 12.27 15.28 25.21 33.69 44.68
52.6 44.1 36.1 12.2 - 0.6 - 2.2 - 3.5 - 4.5" - 4.8 - 2.9
I
Weight
'% amine
47.54 60.40 64.06 73.33 78.69 82.15 85.83 89.26 93.25
T y v ,
C.
-
1.5 4.2 8.0 17.5 24.7 31 $ 2 39.0 49.0 74.8
a Cpon cooling t o -5.0" the first blue opalescence was noted a t -4.9'. ____-
(6) See Glasstone, ref 2, p. 713. (7) Walton and Jenkins, THISJ O U R N A 45, L , 2535 (1923).
3093
C R Y S T A L S T R U C T U R E OF dl-k\LANINE
Aug., 1941
perature of the amine (277') but, since the critical temperature of the mixture is evidently higher than 277', it may be possible that an upper critical solution temperature exists. Results of the study of the three-component system are given in Table I1 and the solubility curve for this system a t 25' is shown in Fig. 2. The broken part of the curve represents those compositions where the transition temperature was found to be indistinct. The composition corresponding to a maximum in the curve is approximately 31.5% amine, 26.5% ethanol, and 42.0% water. TABLE I1 MUTUAL SOLUBILITIES OF AXINE A N D ETHANOL IN WATER Weight, % amine
Weight yo ethanol
Weight, yo amine
Weight, % ethanol
77.6 68.9 G7.2 63.8 62.9 60.9
